This invention relates generally to a removable cap for closing a container of liquid while venting the container to atmosphere in order to allow air to escape from the container.
More specifically, the invention relates to a cap for closing the reservoir of the master cylinder of a surge brake actuator of the type disclosed, for example, in Huetsch et al. U.S. Pat. No. 4,223,766. Such an actuator is mounted on the tongue of a trailer and operates the master cylinder to apply the trailer brakes automatically when the trailer surges forwardly and tends to overrun the towing vehicle. In some cases, brake fluid in the reservoir of the master cylinder overflows into the cap and, to enable the cap to receive the fluid, it is necessary that the cap be vented to atmosphere by means of a passage in the cap. Being carried on the tongue of the trailer, the cap is subjected to dirt, grease, water and other foreign material which tends to plug the vent passage and/or enter into the reservoir by way of the vent passage.